Retractor locking mechanism

ABSTRACT

A retractor for a vehicle restraint system has a locking mechanism comprising an additional inertia member (7) which decouples from the webbing spool when a predetemined acceleration or deceleration force is exceeded, due to the pretensioning operation taking place, and operates a locking pawl (3) to prevent further movement of the spool. The locking pawl (3) is then positively held in the locking condition using a spring catch (9) integral with the inertia member (7), or it can be spring biased in the locking condition using a spring displacing the inertia member (7) against the locking pawl (3) once shear pins (8) have been destroyed. This prevents webbing payout in a multiple crash situation, and provides a positive indication that the pretensioner has fired.

BACKGROUND AND SUMMARY OF THE INVENTION

The present invention relates to a retractor locking mechanism forvehicle safety restraints and particularly to such a mechanism for aretractor fitted a with pretensioner.

Known retractors for vehicle safety restraints have two sensors. Aso-called vehicle sensor detects rapid acceleration or deceleration ofthe vehicle, indicative of a crash situation, and operates a lockingmechanism in response to such a condition to prevent further webbingwithdrawal from the retractor. A webbing sensor traditionally uses aninertia disc rotating with the spool to detect rapid withdrawal ofwebbing, again indicative of a crash situation, and to lock the webbingspool against further rotation in response to such rapid withdrawal.

Recently pretensioning systems have been incorporated to improve safetyrestraints. These devices take up slack in the webbing to more securelylocate the vehicle occupant in his seat in the event of a crash. Rapidacceleration or deceleration of a vehicle typically triggers anexplosive device to pull a cable and rapidly rotate the retractor spoolin a webbing winding direction. A webbing intake of 200 mm inapproximately 10 ms is required for the pretensioner to be effective.

At these rates of acceleration the applicant has observed that the websensor is prelocked by the operation of the pretensioner.

The web sensor has an earlier phasing geometry than the vehicle sensorso that it tends to cause engagement of the main locking member earlierthan the vehicle sensor does.

It is an object of the present invention to take advantage of theearlier phasing geometry of the webbing sensor and to provide a lockingmechanism which is actuated via the webbing sensor and which locks theretractor spool permanently against further webbing withdrawal. Such alocking mechanism has the advantage of preventing webbing payout in amultiple crash situation and of being a tangible sign that apretensioner has fired and preventing re-use of the retractor after anaccident.

According to the present invention there is provided a locking mechanismfor a webbing retractor for a vehicle safety restraint system, theretractor comprising safety restraint webbing wound on a rotatablespool, and on inertia member mounted for rotation with the spool undernormal usage conditions and means coupling the inertia member to thespool so that it rotates with the spool under normal usage conditions,and is decouplable by acceleration or deceleration forces above apredetermined level (e.g. indicative of a pretensioning operation) todecouple the inertia members and the spool and wherein holding means areoperable by the inertia member to hold a locking pawl in lockingengagement with the spool to lock the spool against rotation.

Preferably the retractor comprises a web sensor having a web sensorinertia element mounted to rotate with the spool and the inertia memberunder normal usage conditions and resiliently connected to the lockingpaw in such a way that when the spool is rotated faster that apredetermined speed the inertia element lags the spool and via theresilient means moves the locking pawl into locking engagement with thespool to lock the spool against rotation.

Preferably the coupling means comprise shear pins or deformable elementswhich nay be formed integrally with the inertia member and which shearor bend respectively under high acceleration or deceleration forces toallow rotation of the inertia member independently of the spool.Advantageously the shear pins are located in indentations or blind holesto prevent the loose parts fouling the retractor mechanism after theyhave fractured.

According to a particular preferred embodiment the holding meanscomprises an integrally moulded detent on the second inertia member. Theinertia member may be provided with a spring bias adapted to bias theholding means to lock onto the locking means on operation of themechanism of the invention. This bias could be a coiled torsion springlinking the inertia member to the web sensor inertia element. A springcatch may also be provided to positively lock the locking means: forexample an integrally moulded clip on the inertia member. Parts of themechanism may be made of zinc casting or of moulded plastic materials.

The coupling between the inertia member and the web sensor inertiaelement (which may each be of a general disc form) is such that duringnormal operation of the retractor, the inertia mean member plays no partin the function of the web sensor (and its inertia element) because theangular accelerations experienced by the mechanism during normaloperation are too low to cause decoupling eg. to shear the connectingpins or deform the deformable coupling.

For a better understanding of the present invention and to show how thesame may be carried into effect, reference will now be made to theaccompanying drawings in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1-3 are cross sectional views of a mechanism according to theinvention under conditions corresponding to normal retractor operation,web sensor normal lock and web sensor pretensioning lock respectively.

FIGS. 4a and 4b are cross sectional side and schematic plan viewsrespectively of parts of a preferred embodiment of the invention.

FIG. 5 is an enlarged view of part of a preferred embodiment themechanism of the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

In FIG. 1 a cross sectional side view of a mechanism according to theinvention is shown. The end of the spool is shown at 1 and on this ismounted a web sensor inertia member or element, such as disc which undernormal conditions of use of the retractor rotates with the spool. Theoperation of the web sensor inertia disc is well known to anyone workingin the field of retractors. It is connected to the spool by resilientmeans such as a spring and under conditions of high acceleration i.e.when the webbing is unwound suddenly as in a crash situation, theinertia disc 2 lags behind the spool and operates a pawl 3 to lock thespool against further rotation. This pawl engages teeth 4 on the insideof the end of the spool 1 and subsequently a load bearing lockbar 5 isbrought into engagement with the lock cup 6 to prevent webbing payoutfrom the spool in a crash condition.

According to the invention, a second inertia member or element, such asa disc 7 is coaxially mounted with the first inertia disc 2 and isconnected thereto by shear pins 8. Under conditions of particularly highdeceleration, such as after firing of a pretensioner, the angularaccelerations are sufficient to break the shear pins 8 and to allow thesecond inertia disc 7 to rotate (clockwise as shown in FIG. 1). Uponrotation, one of the extensions 9 on the second inertia disc engageslocking pawl 3 and holds it in the spool locking position. This sequenceis shown in FIGS. 1-3 where like features are identified by likereference numerals. FIG. 1 shows the web sensor in a rest position withthe pawl 3 disengaged. This is the situation during normal operation ofthe retractor. In a crash situation the first inertia disc 1 lags behindthe spool, and moves relative to the spool in a clockwise direction asshown in FIG. 2 by arrow A. In the position shown in FIG. 2 it engagespawl 3, moving it against the action of spring 10 into engagement withthe teeth 4 on the inside of the spool. If the crash situation hasactivated the pretensioner then the acceleration forces will be suchthat the shear pins 8 break and the second inertia disc 7 rotatesfurther in direction A so that extension 9 moves to engage pawl 3,behind the pawl post 12 so as to hold the pawl 3 in a locking position.Hence if further, crashes are experienced for example in the event of amultiple vehicle pile up, the retractor will not release any morewebbing and the vehicle occupant is securely restrained in his seat.

FIGS. 4a and 4b show a preferred embodiment of the invention wherein thefirst inertia disc 1 is linked to the second inertia disc 7 by a coiledtorsion spring or similar bias means 13. This torsion spring acts topush the second inertia disc 7 into holding engagement with the websensor pawl 3 once the shear pins 8 have broken.

FIG. 5 illustrates an additional clip element 14 which might form anintegral part of the extension 9 of the second inertia disc 7. Ondeployment of the second inertia disc in a pretensioning situation thisadditional clip element 14 engages the post 12 on the web sensor pawl tolock the web sensor pawl in a spool engagement position.

What is claimed is:
 1. A webbing retractor for a vehicle safetyrestraint system, the retractor comprising safety restraint webbingwound on a rotatable spool, and a locking mechanism comprising a firstinertia member and a second inertia member rotatable with the firstinertia member, first coupling means arranged to couple the firstinertia member to the spool so that the first and the second inertiamembers rotate with the spool under normal usage conditions, andarranged to decouple the first inertia member from the spool uponrotational acceleration or deceleration of the spool above apredetermined level, second coupling means for decoupling the secondinertia member from the first inertia member at excessive levels ofacceleration or deceleration of the spool, and holding means operableupon decoupling of the second inertia member from the first inertiamember for holding a pawl in locking engagement with the spool to affectthe locking up of the spool against rotation even after cessation of theacceleration or deceleration forces.
 2. A webbing retractor as claimedin claim 1, in which parts of the locking mechanism are made of zinccasting or of moulded plastic materials.
 3. A webbing retractor asclaimed in claim 1 in which the second coupling means comprises shearpins or deformable elements which are arranged to shear or bendrespectively under acceleration or deceleration forces above apredetermined level to allow rotation of the inertia memberindependently of the spool.
 4. A webbing retractor for a vehicle safetyrestraint system, the retractor comprising safety restraint webbingwound on a rotatable spool, and a locking mechanism comprising aninertia member, coupling means arranged to couple the inertia member tothe spool so that it rotates with the spool under normal usageconditions, and arranged to decouple the inertia member from the spoolupon rotational acceleration or deceleration of the spool above apredetermined level, and holding means operable by the inert in memberupon decoupling from the spool to hold a locking pawl in lockingengagement with the spool to lock the spool against rotation;in whichthe coupling means comprises shear pins or deformable elements which arearranged to shear or bend respectively under acceleration ordeceleration forces above a predetermined level to allow rotation of theinertia member independently of the spool.
 5. A webbing retractor asclaimed in claim 4, in which the shear pins are located in indentationsor blind holes arranged to prevent loose parts fouling the retractormechanism after they have sheared.
 6. A webbing retractor as claimed inclaim 5, in which the shear pins or deformable elements are formedintegrally with the inertia member.
 7. A webbing retractor as claimed inclaim 4, in which the shear pins or deformable elements are formedintegrally with the inertia member.
 8. A webbing retractor for a vehiclesafety restraint system, the retractor comprising safety restraintwebbing wound on a rotatable spool, and a locking mechanism comprisingan inertia member, coupling means arranged to couple the inertia memberto the spool so that it rotates with the spool under normal usageconditions, and arranged to decouple the inertia member from the spoolupon rotational acceleration or deceleration of the spool above apredetermined level, and holding means operable by the inertia memberupon decoupling from the spool to hold a locking pawl in lockingengagement with the spool to lock the spool against rotation;in whichthe holding means comprises one of an integrally moulded detent and clipon the inertia member.
 9. A webbing retractor for a vehicle safetyrestraint system, the retractor comprising safety restraint webbingwound on a rotatable spool, and a locking mechanism comprising a firstinertia member and a second inertia member rotatable with the firstinertia member, first coupling means arranged to couple the firstinertia member to the spool so that the first and the second inertiamembers rotate with the spool under normal usage conditions, andarranged to acceleration or deceleration of the spool above apredetermined level, second coupling means for decoupling the secondinertia member from the first inertia member at excessive levels ofacceleration or deceleration of the spool, and holding means operableupon decoupling of the second inertia member from the first inertiamember for holding a pawl in locking engagement with the spool to causethe locking of the spool against rotation; anda spring for biasing thesecond inertia member in a direction so that the holding means remainsurged against the pawl.
 10. A webbing retractor as claimed in claim 9,in which the spring bias is provided by a coiled torsion spring linkingthe inertia member to the web sensor inertia element.
 11. A webbingretractor for a vehicle safety restraint system, the retractorcomprising safety restraint webbing wound on a rotatable spool, and alocking mechanism comprising an inertia member, coupling means arrangedto couple the inertia member to the spool so that it rotates with thespool under normal usage conditions, and arranged to decouple theinertia member from the spool upon rotational acceleration ordeceleration of the spool above a predetermined level, and holding meansoperable by the inertia member upon decoupling from the spool to hold alocking pawl in locking engagement with the spool to lock the spoolagainst rotation;comprising a spring catch arranged positively to lockthe locking mechanism.
 12. A webbing retractor as claimed in claim 11,in which the spring catch comprise s an integrally moulded clip on theinertia member.
 13. A webbing retractor for a vehicle safety restraintsystem, the retractor comprising safety restraint webbing wound on arotatable spool, and a locking mechanism comprising a first inertiamember and a second inertia member rotatable with the first inertiamember, first coupling means arranged to couple the first inertia memberto the spool so that the first and the second inertia members rotatewith the spool under normal usage conditiones, and arranged to decouplethe first inertia member from the spool upon rotational acceleration ordeceleration of the spool above a predetermined level, second couplingmeans for decoupling the second inertia member from the first inertiamember at excessive levels of acceleration or deceleration of the spool,and holding means operable upon decoupling of the second inertia memberfrom the first inertia member for holding a pawl in locking engagementwith the spool to cause the locking of the spool against rotation;andwherein the first and second inertia members are positioned inrespective, generally parallel planes.
 14. The webbing retractor asdefined in claim 13 wherein the first and second inertia members aredisc-shaped.
 15. A webbing retractor for a vehicle safety restraintsystem, the retractor comprising safety restraint webbing wound on arotatable spool, and a locking mechanism comprising an inertia member,coupling means arranged to couple the inertia member to the spool sothat it rotates with the spool under normal usage conditions, andarranged to decouple the inertia member from the spool upon rotationalacceleration or deceleration of the spool above a predetermined level,and holding means operable by the inertia member upon decoupling fromthe spool to hold a locking pawl in locking engagement with the spool tolock the spool against rotation;in which the predetermined levelcorresponds to that produced by a pretensioning operation of theretractor.
 16. A webbing retractor for a vehicle safety restraintsystem, the retractor comprisingsafety restraint webbing wound on arotatable spool, a lock bar rotatably disposed relative to a retractorframe and movable under the operation of a lock cup, the lock cup beingdecoupled from the spool during normal operation of the retractor andlinked to move with the spool during other operating conditions, thelock bar movable from an unlocked position to a locked position to stopthe spool from rotating; a web sensor having a first inertia member anda web sensor pawl, the first inertia element being mounted to rotatewith the spool under normal operating conditions, wherein under otheroperating conditions the position of the first inertia member lags theposition of the spool to move the web sensor pawl to couple the spoolwith the lock ring enabling the lock ring to move the lock pawl to stopthe spool, the web sensor further including a second inertia memberwhich is movable against the web sensor pawl upon rotationalacceleration or deceleration of the spool above a predetermined level tohold a web sensor pawl in its engaged position to maintain the spool ina locked condition.